Purpose

Use the LOCKTABLE statement to lock one or more tables (or table partitions or subpartitions) in a specified mode. This lock manually overrides automatic locking and permits or denies access to a table or view by other users for the duration of your operation.

Some forms of locks can be placed on the same table at the same time. Other locks allow only one lock for a table.

A locked table remains locked until you either commit your transaction or roll it back, either entirely or to a savepoint before you locked the table.

A lock never prevents other users from querying the table. A query never places a lock on a table. Readers never block writers and writers never block readers.

Syntax

Keywords and Parameters

schema

Specify the schema containing the table or view. If you omit schema, Oracle assumes the table or view is in your own schema.

table / view

Specify the name of the table to be locked.

If you specify view, Oracle locks the view's base tables.

If you specify PARTITION (partition) or SUBPARTITION (subpartition), Oracle first acquires an implicit lock on the table. The table lock is the same as the lock you specify for partition or subpartition, with two exceptions:

If you specify a SHARE lock for the subpartition, Oracle acquires an implicit ROWSHARE lock on the table.

If you specify an EXCLUSIVE lock for the subpartition, Oracle acquires an implicit ROWEXCLUSIVE lock on the table.

If you specify PARTITION and table is composite-partitioned, then Oracle acquires locks on all the subpartitions of partition.

Restriction: If table is part of a hierarchy, it must be the root of the hierarchy.

dblink

Specify a database link to a remote Oracle database where the table or view is located. You can lock tables and views on a remote database only if you are using Oracle's distributed functionality. All tables locked by a LOCKTABLE statement must be on the same database.

If you omit dblink, Oracle assumes the table or view is on the local database.

lockmode Clause

Specify one of the following modes:

ROW SHARE

ROWSHARE permits concurrent access to the locked table, but prohibits users from locking the entire table for exclusive access. ROWSHARE is synonymous with SHAREUPDATE, which is included for compatibility with earlier versions of Oracle.

ROW EXCLUSIVE

ROWEXCLUSIVE is the same as ROWSHARE, but also prohibits locking in SHARE mode. ROWEXCLUSIVE locks are automatically obtained when updating, inserting, or deleting.

SHARE UPDATE

SHARE

SHARE ROW EXCLUSIVE

SHAREROWEXCLUSIVE is used to look at a whole table and to allow others to look at rows in the table but to prohibit others from locking the table in SHARE mode or updating rows.

EXCLUSIVE

EXCLUSIVE permits queries on the locked table but prohibits any other activity on it.

NOWAIT

Specify NOWAIT if you want Oracle to return control to you immediately if the specified table (or specified partition or subpartition) is already locked by another user. In this case, Oracle returns a message indicating that the table, partition, or subpartition is already locked by another user.

If you omit this clause, Oracle waits until the table is available, locks it, and returns control to you.

Examples

LOCKTABLE Example

The following statement locks the employees table in exclusive mode, but does not wait if another user already has locked the table:

LOCK TABLE employees

IN EXCLUSIVE MODE
NOWAIT;

The following statement locks the remote accounts table that is accessible through the database link boston: